1. Field of the Invention
This invention relates to a sheet-shaped adhesive silicone composition.
2. Prior Art
Adhesives have been used in a wide variety of industrial fields including aircraft, space, vehicle, ship, construction, building, electric and electronic fields. Inter alia, silicone adhesives have improved heat resistance, freeze resistance, weather resistance and electrical insulation and are advantageously used in applications where conventional adhesives could not be utilized.
Most conventional silicone adhesives, however, are filled in tubes and cartridges since they are liquid or paste. The silicone adhesives are generally classified into two groups, (i) those adhesives like silicone sealants which crosslink into an elastomer through reaction with moisture in air and bond to adherends through condensation reaction of hydrolyzable silane and (ii) those adhesives which are prevented from reaction by inhibitors during storage, but crosslink into an elastomer upon heating on use and bond to adherends through addition reaction of adhesive aids promoted by platinum catalysts. Since these silicone adhesives are liquid or paste and sticky, many inconvenient problems arise. They stick to the hand and adhere to and stain unnecessary portions upon accidental contact. They are inconvenient to handle. Where parts are to be bonded, fine adjustment or alignment is difficult. The adhesive cannot be applied to a uniform thickness. If the adhesive is moved during cure, air can penetrate into the adhesive to weaken the bond strength or exacerbate the insulating function.
To overcome these problems, JP-A 141972/1989 proposes a film-shaped silicone adhesive composition using hydrophobic reinforcing silica prepared by a wet process. This film-shaped silicone adhesive composition is satisfactorily applicable to such adherends as glass and silicone rubber, but fail to provide an acceptable bond strength when applied to such adherends as metals and plastics. The silica used therein is not readily available.